Prior Art
In an earlier U.S. patent application entitled "CELL BASED WIDE AREA NETWORK ALTERNATIVE ACCESS TELEPHONE AND DATA SYSTEM" having Ser. No. 07/953,744, filed on Sep. 29, 1992, by the same inventor as the present application, an ATM compliant cell based communications network is described. That network uses a bi-directional fiber transmission path to a conventional feeder cable TV system to a shared radio channel to poll a multiplicity of cordless telephones and other devices. In that earlier patent application, a multiplicity of separate frequency division channels, each carries a 2 Mb/s signal to and from each set top SIU (Subscriber Interface Unit) unit to the FTU (Fiber Terminating Unit) located at the cable TV system head-end. In that application, the upstream (toward the headend) transmission is limited to the 5-30 MHz range, a de facto standard upstream band as commonly used by the cable TV industry today. The downstream cells are carried within the cable's normal TV broadcast band.
Having a capacity of only about 25 MHz available in the upstream channel is very limiting since very high data rates are required to connect LANS (Local Area Networks), for example. Compounding this restriction, only about 12 MHz is truly available since (1) it is necessary to use this band to support other upstream cable TV services, and (2) it is necessary to avoid frequencies carrying HF broadcast and amateur signals that also use this band, as strong signals can leak into the feeder cable if the flexible drop cable sheaths weather and fracture and/or connectors become loose. A multiplicity of simultaneous 2 Mb/s signals, each on a separate 533 KHz FDM (Frequency Division Multiplexed) carrier are multiplexed together in that system. This further requires low-distortion analog transmission and requires the use of expensive analog signal optic fiber transmitters and receivers, rather than lower cost simpler digital fiber arrangements that are used in the present invention. Further, additional equipment is required upstream by the prior invention to multiplex and de-multiplex each 0.533 MHz carrier.
In the prior referenced patent application, a novel form of dynamic polling was used that was limited solely to dynamically polling nearby radio devices. In that application the total shared data rate of the polled devices was only 2 Mb/s. And, the distances were on the order of a hundred feet or so, which permitted an efficient polling technique. However, when the data rate is increased to the order of 100 Mb/s, and where distances can be in several kilometers rather than tens of meters, then a new form of polling becomes necessary. The known options for sharing bus structure include polling, token passing and random access with collision retransmission. As the ATM cell packet is short, the data rate high, and path length long, simple polling requires too long a time between allowable transmissions to be efficient. Token passing is better suited to a peer-to-peer configuration and not appropriate to the present many-to-one architecture, i.e. many SIUs and one FTU. And, random access with collisions does not provide the guarantee of delivery to support voice in an optimal manner.
The present invention overcomes these earlier limitations by significantly increasing the allowable upstream data rate from each subscriber in the system using frequencies otherwise not usable. A common shared high speed digital transmission channel is used in lieu of multiple FDM 533 KHz carriers. The overall capacity is increased and the number of components and their cost significantly reduced by using a PON (Passive Optic Network) fiber optic path which does not require active components, and offers improved reliability. The band of rf frequencies available above the range of the cable TV amplifier that can pass through the taps and coaxial cable, not otherwise usable, is generally wide. In many cases, it is able to support a common, shared channel in the 45 to 155 Mb/s range. To effectively share this common channel, a new multiplexing approach has been created to load balance each SIU competing for the single shared channel capacity.